1. Field of the Invention
The present invention relates to an ink jet recording apparatus for discharging ink from discharge ports of an ink jet recording head to perform recording.
2. Related Background Art
Recording apparatuses such as printers, copying machines, facsimile systems, and the like, which are used together with computers or wordprocessors, or are used individually , feed and convey sheet-like recording media such as paper sheets or plastic thin plates, and record images on the recording media on the basis of image information. The recording apparatuses can be classified into an ink jet system, a wire-dot system, a thermal system, a laser beam system, and the like depending on their recording systems.
Of these systems, the ink jet recording system (ink jet recording apparatus) causes recording means (recording head) to discharge ink toward a recording medium to perform recording. The ink jet recording system has the following advantages. That is, the system can record a high-quality image at high speed, and can perform recording on normal paper without always requiring special treatment. Since the ink jet recording system is a non-impact system, noise is low, and it is easy to record a color image using many color inks. Of the ink jet recording system, an ink jet recording apparatus employing a line-type recording means in which a large number of discharge ports are aligned in the widthwise direction of a paper sheet can attain recording operations at a higher speed.
In particular, in an ink jet recording means (recording head) which uses heat energy as energy for discharging ink, electrothermal transducers which are formed on a substrate via semiconductor manufacturing processes such as etching, deposition, sputtering, and the like, liquid path walls, a top plate, and the like are formed, so that a recording head having a high-density liquid path arrangement (discharge port arrangement) can be easily manufactured.
Such an ink jet recording apparatus normally comprises an arrangement for keeping a satisfactory ink discharging state by preventing an increase in ink viscosity due to evaporation of an aqueous ink component in discharge ports or a portion around them where a recording liquid (ink) contacts air, or by removing an ink whose viscosity is increased.
In particular, in a recording head of a type for discharging an ink by utilizing heat energy, since discharge ports and liquid paths communicating with the ports can be arranged very precisely at a high density, the influence of an increase in ink viscosity tends to be relatively increased.
For this reason, each of these ink jet recording apparatuses comprises a capping mechanism for covering and closing (capping) a surface where discharge ports of a recording head are arranged in a non-recording operation state during which no ink is discharged, thereby preventing evaporation of an aqueous ink component from the discharge ports. In order to assure stable ink discharge, ink is periodically discharged from all or desired discharge ports of a recording head at a predetermined position during, e.g., a recording operation, thus performing so-called preliminary discharge (idle discharge) for renewing an ink in particular discharge ports which are not involved in recording. In addition, an ink absorbing recover or ink compression recover operation for discharging a viscosity-increased ink or a foreign matter by absorbing or compressing an ink in the discharge ports at the beginning of recording or at predetermined time intervals is performed.
However, for example, when capping of an ink jet recording head is performed by executing a series of power-off sequences, a circuit for operating an activating source such as a motor for a predetermined period of time by, e.g., a relay is required, resulting in a complex apparatus arrangement. In addition, upon completion of a recording operation, a power source cannot be turned off until the power-off sequences are completed, resulting in an inconvenience. Furthermore, in this case, attachment of a foreign matter or dust can be prevented by capping the ink jet recording head. However, since an increase in viscosity of an ink in the ink jet recording head cannot be satisfactorily prevented, this may cause a discharge error including an ink non-discharge state in the next recording operation.
When ink is forcibly discharged upon a power-on operation of the ink jet recording apparatus, a fixed amount of ink is always discharged although the degree of increase in viscosity of ink in the ink jet recording head varies depending on the non-use time of the ink jet recording apparatus. For this reason, when a power source is frequently turned on/off, steps against waste of an ink, an increase in running cost, contamination of the interior of the apparatus due to the discharged ink, and the like must be taken.
Furthermore, since recover operations such as absorbing, compression, and idle discharge operations are added, time is wasted in addition to an original recording time, and as the result, a recording speed is undesirably lowered.
Moreover, when an ink jet recording apparatus is left for a long period of time while its power source is kept OFF, or is left in a low-temperature condition, a discharge error (e.g., unstable discharge or non-discharge state) may occur due to an increase in viscosity of an ink or sticking of an ink in the ink discharge ports. As a method of solving this problem, sequences for performing recover operations of a recording means (recording head) upon a power-on operation are performed, as described above. In the conventional power-on recover operations, an absorbing recover operation is constantly performed regardless of the environmental temperature of the recording means, or the temperature around the recording means is detected only upon a power-on operation, and the number of times the absorbing recover operation is conducted is increased/decreased according to the detected temperature, thus changing a treatment level.
However, in the conventional recover method, judgment of an ink sticking state in the discharge ports can only be made by a detected temperature around the recording means upon a power-on operation. For example, when an abrupt change in temperature occurs immediately before use of the recording apparatus, or when the recording apparatus is left in a low-temperature state for a long period of time before the power source is turned on, it is impossible to correctly determine an ink sticking state of the recording means (recording head). FIG. 25 is a graph for exemplifying a change in temperature when a temperature of the recording means is abruptly increased immediately before the recording apparatus is used, and FIG. 26 is a graph for exemplifying a change in temperature of the recording means when the apparatus is left in a low-temperature state for a long period of time before the power source is turned on. In FIGS. 25 and 26, a standard temperature corresponds to a temperature at which an ink sticking phenomenon begins below this temperature.
For these reasons, the conventional control method of recover operations of the recording means cannot determine an ink sticking state upon a power-on operation due to a hysteresis temperature before the power source is turned on. Therefore, since the recover operations upon a power-on operation cannot be performed according to an actual ink sticking state, control becomes unsatisfactory. As a result, an ink discharging state in recording becomes unstable, and recording quality cannot be maintained. In order to guarantee stability of an ink discharging state, recover operations must be excessively performed, and waste of ink and time cannot be avoided.